Hello. I have an old working PSU. I use it for 2 small fans. Can i only use the Purple wire to power 2 small fans for 21 days? Will the power suply overheat?
Can i use it with out green wire (green wire turns on the power suply)?
Not really intended for such a low power load. some older PSU designs can have a problem with that. You would need to measure each voltage output to see if that is the case here. Unbalanced load can lead to very high 12V output if I recall correctly.
You shouldn't use the green wire for power. That is basically the on switch. It sits at 5V waiting to be shorted to ground to let the PSU know to turn on.
If you are running 5V fans, or want to run 12V fans at 5V pick one of the red wires for 5V. Yellow for 12V.
Simply the green the wire to a nearby black wire to turn the power supply on permanently.
That said, I have wired up an old USB charging brick to act as a fan tester. Just outputs 5V to see if they'll spin. And you could do something similar, or an old 12v or 9V power brick.